CONVECTIVE FORECAST
VALID 06Z SUN 09/06 - 06Z MON 10/06 2003
ISSUED: 08/06 01:36Z
FORECASTER: GROENEMEIJER
+++ CORRECTED +++

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS DENMARK, EXTREME NORTHERN GERMANY AND THE NORTHEASTERN NETHERLANDS.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHWESTERN FRANCE, EXTREME SOUTHEASTERN ENGLAND, WESTERN AND NORTHERN GERMANY, NORTHWESTERN POLAND, DENMARK AND SOUTHERN SWEDEN.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS MUCH OF WESTERN AND CENTRAL EUROPE, THE WESTERN BALKANS, THE SOUTHEASTERN BRITISH ISLES, SOUTHERN SCANDINAVIA AND SOUTHERN TURKEY.

SYNOPSIS

WITHIN A SOUTHWESTERLY JET STREAM AN INTENSE TROUGH IS PRESENT FROM THE WESTERN BRITISH ISLES NEAR THE BAY OF BISCAY, MOVING EASTWARD. A FRONTAL ZONE IS LOCATED NEAR THE AXIS OF THE JET DOWNSTREAM OF THE TROUGH. WATER VAPOUR IMAGERY SHOWS THAT A WAVE IS STARTING TO DEVELOP WITHIN THIS FRONTAL ZONE.

DISCUSSION

...FRANCE, ENGLAND, BENELUX, GERMANY, DENMARK, SWEDEN AND POLAND...
THERE WILL BE TWO CATEGORIES OF CONVECTION IN THIS FORECAST PERIOD. THE FIRST IS PREFRONTAL CONVECTION AND SECOND IS CONVECTION ALONG THE COLD FRONT.

PREFRONTAL CONVECTION WILL LIKELY INITIATE OVER NW FRANCE DURING THE EARLY MORNING NEAR A PREFRONTAL CONVERGENCE LINE. EXPECT SOME SCATTERED STORMS TO FORM OVER THE BENELUX, WESTERN GERMANY AND MUCH OF DENMARK LATER DURING MORNING. STORMS OVER FRANCE AND THE BENELUX WILL BE ELEVATED AT FIRST, BUT SHOULD ROOT INTO THE BOUNDARY LAYER DURING THE AFTERNOON. GIVEN STRONG DEEP-LAYER SHEAR, THE ANTICIPATED MODE OF THE STORMS WILL BE (ELEVATED) SUPERCELLS CAPABLE OF PRODUCING HAIL, THAT COULD REACH THE SEVERE LIMIT OF 2 CM DIAMETER IN SOME, AND SOME STRONG GUSTS.

STORMS FORMING OVER THE NORTHEAST OF THE NETHERLANDS, NORTHWESTERN GERMANY AND IN PARTICULAR THOSE OVER DENMARK WILL LIKELY BE ABLE TO HAVE MORE HELICAL LOW-LEVEL INFLOWS, AS SURFACE WINDS WILL BE MORE BACKED TOWARDS THE NORTH. STORMS FORMING OVER DENMARK NEAR THE WARM FRONT WILL HAVE A MORE SIGNIFICANT TORNADO THREAT GIVEN FORECAST LOW LCL HEIGHTS AND EASTERLY SURFACE WINDS SUPPLYING LOW-LEVEL HELICITY. AS THE CONVECTION OF DENMARK CLUSTERS INTO AN MCS...AS SUGGESTED BY VARIOUS NUMERICAL MODELS...TORNADIC THREAT WILL DEMINISH. THE MCS SHOULD TRACK EASTWARD AND AFFECT SOUTHERN SWEDEN IN THE EVENING AND OVERNIGHT WITH STRONG TO SEVERE WIND GUSTS AND A GRADUALLY DECREASING THREAT OF HAIL. THE THREAT OF TORNADOES WITH THE STORMS FORMING OVER THE NETHERLANDS AND GERMANY, SEEMS TO BE SMALLER SINCE LCL HEIGHTS WILL NOT BE AS LOW AND SURFACE WIND MAY NOT BE AS MUCH BACKED AS NEAR THE WARM FRONT OVER DENMARK. HOWEVER, 00Z OBSERVATIONS SHOW THE PRENSENCE OF AN OLD SEA BREEZE FRONT LOCATED NEAR A LINE FROM BRUSSELS TO MAASTRICHT TO OSNABRUECK TO BREMEN, THAT MAY PROVIDE CONSIDERABLE HIGHER HELICITY TO STORMS FORMING NEAR THIS BOUNDARY. IF THE BOUNDARY PERSISTS DURING THE MORNING HOURS, ANTICIPATE ENHANCED STORM ROTATION AND SEVERE WEATHER THREAT WHEN STORMS INTERACT WITH THE BOUNDARY, POSSIBLY INCLUDING A THREAT OF TORNADOES.

ALONG THE COLD FRONT, LOCATED OVER THE SOUTHERN NORTH SEA AND THE ENGLISH CHANNEL REGION INTO NORTHWESTERN FRANCE, CONVECTION WILL INITIATE IN THE MORNING AND AFTERNOON. STRONG DYNAMIC FORCING FOR UPWARD VERTICAL MOTION AT THE FRONT AND SMALL DIRECTIONAL SHEAR INDICATE THAT THE CONVECTION WILL RAPIDLY ORGANISE INTO A LINEAR MCS. THE MCS WILL BE CAPABLE OF PRODUCING STRONG TO SEVERE WIND GUSTS AND LARGE HAIL. THE LINE WILL RAPIDLY SURGE EASTWARD OVER THE NETHERLANDS. AS THE LOW-LEVEL BACKGROUND WINDS NEAR THE SQUALL-LINE ARE EXPECTED TO INCREASE SOMEWHAT OVER TIME....AND POTENTIAL FOR EVAPORATIONAL SUPPORT FOR COLD-POOL FORMATION WILL INCREASE DUE TO INGESTION OF LOWER BOUNDARY-LAYER MOISTURE...SEVERE WIND THREAT WILL INCREASE. THE SQUALL-LINE WILL REACH NORTHERN GERMANY IN THE EVENING AND EARLY NIGHT. LOWER INSTABILITY WILL THEN DEMINISH SEVERE WIND THREAT SOMEWHAT BEFORE THE SYSTEM AFFECTS NORTHERN POLAND OVERNIGHT INTO EARLY TUESDAY MORNING.

HAVE DECIDED TO PLACE A MDT RISK OVER AREAS MOST LIKELY TO EXPERICENCE SEVERE (>50KT) STRAIGHT-LINE WINDS OVER NETHERLANDS AND GERMANY AND OVER PARTS OF DENMARK WHERE THREAT OF TORNADOES IS LARGEST.

...ITALY AND THE BALKANS...
SUBSTANTIAL INSTABILITY WILL BE PRESENT BOTH OVER NORTHERN ITALY AS WELL AS OVER MUCH OF THE WESTERN BALKANS. HOWEVER, SMALL VERTICAL WIND SHEAR INHIBITS THE SEVERE THREAT OF THE WIDESPREAD DEEP MOIST CONVECTION THAT IS EXPECTED TO FORM DURING THE DAY. OCCASIONAL STRONG WIND GUSTS AND HAIL ARE POSSIBLE WITH THE STOMS. INTERACTION OF STORMS AND OUTFLOWS MAY PROVIDE FOCI OF MORE INTENSE SEVERE EVENTS, THAT MAY REACH SEVERE LEVELS. HOWEVER, THE OVERALL THREAT IS TOO LOW TO WARRANT A CATEGORICAL RISK.

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